1. Field of the Invention
The present invention is directed to an improved injection nozzle for a metallic material injection-molding machine and particularly a metal alloy injection machine.
2. Related Prior Art
In metallic material injection technology the facing surfaces between the nozzle and the sprue bushing on the mold have been machined so as to be compliant with one another and designed so as to have substantial surface contact. In this design it was assumed that the carriage cylinders could apply sufficient pressure to the nozzle to prevent it from parting contact with the sprue bushing. However, it has been discovered that even when the highest acceptable force is applied at the interface between the nozzle and the sprue bushing, it is insufficient to prevent some parting at the interface. This parting at the interface creates a build up of injection material on the surfaces of the interface with the ultimate result that the interface may fail to seal and permit the leakage of the injected material with sometimes catastrophic results.
In the prior art designs, the mating geometry between the faces of the nozzle and the sprue bushing were designed to withstand the positive forces applied by the carriage cylinders and remain in positive sealing contact throughout a complete machine cycle. The mating surfaces of the nozzle and the sprue bushing might be flat, spherical, conical or any other geometric shape that would provide an acceptable area of positive contact. The positive force applied by the carriage cylinders to the interface between the sprue bushing and the nozzle was intended to overcome the reactive forces developed as a result of the injection pressure generated during injection and any dynamic forces created as a result of any energy transfer between the components of the machine involved in the injection process.
Unfortunately, it has been discovered that it is virtually impossible to provide adequate clamping force to prevent separation between the nozzle and the sprue bushing when injecting metallic material, particularly material in a thixotropic state, because such very high pressures are involved and the reactionary and dynamic forces reach such high and relatively uncontrolled levels that separation eventually occurs.
Japanese Patent 11048286 to Japan Steel Works Ltd. is a further example of a nozzle that will continue to have leakage problems when subjected to the injection pressures normally associated with metallic material injection. In that design, the nozzle has a projected cylindrical part that is inserted into a cylindrical recess in the mold. The two annular surfaces formed on the nozzle and the mold are held in annular contact so as to maintain the nozzle to mold interface sealed. It is the problem of maintaining such a seal that has been overcome by the present invention, which does not require that the nozzle be in facing contact with the mold.
The primary objective of the invention is to provide a nozzle to sprue bushing interface in a metallic material injection-molding machine that will remain sealed during the injection cycle.
Another object of the invention is to provide, in a metallic material injection machine, an injection nozzle that may move relative to the sprue bushing without losing sealing at the interface between the nozzle and the bushing.
A further object of the invention is to provide, in a metallic material injection machine, a seal between the machine nozzle and the mold that requires a minimal force to be applied between the mold and the nozzle to maintain a seal between them.
A further object of the invention is to provide, in a metallic material injection machine, a machine nozzle and sprue bushing design that does not require contact between the nozzle and bushing to maintain sealing between them.
The foregoing objects are achieved by extending the nozzle into the interior surface of the sprue bushing.
The invention provides an improved nozzle and sprue bushing for a metallic material injection molding machine. The sprue bushing has a cylindrical surface and the nozzle an annular portion. The annular portion snugly fits within the cylindrical surface to provide a sealing engagement between the surface and the portion when the nozzle engages the bushing. The surface and the portion are of sufficient length to permit limited axial movement therebetween without a loss of sealing between them. The actual seal may be provided by the close fit between the bushing and the nozzle or by slight seepage of the metallic material between the surfaces where it freezes and provides the necessary seal.
The invention provides, in a metallic material injection molding machine, an injection nozzle joined to an injection barrel of the injection molding machine, a stationary platen holding a portion of a mold and a sprue bushing mounted in the mold. The nozzle engages the sprue bushing when the metallic material is injected through the sprue bushing into the mold. The nozzle has a spigot portion which extends into a channel in the sprue bushing. An outer periphery of the spigot fits into the inside surface of the channel so as to create a seal between the surface and the periphery of the spigot or enable the metallic material to create the seal and thereby prevent loss of metallic material through the interface between the nozzle and the sprue bushing during an injection cycle.
The invention is useful in any metallic material injection or casting process that requires a sealed interface between a nozzle and a sprue bushing. The invention has been found particularly useful when injecting metallic alloys such as magnesium based alloys when in the thixotropic state.